In color Doppler, the Doppler shift is measured over an area in the image, instead of only along a line as with spectral Doppler measurement. This produces a 2D image. The mean velocity is color coded and shown overlaid a 2D B-mode image. Additionally, information about turbulence, often an indication of abnormal blood flow, can be depicted. It can be derived from the Dopplershift's bandwidth. As with the Doppler spectrum, the larger the "sample volume", the better the sensitivity, but the poorer the localization. Furthermore, one can change the measurement time in each direction (number of pulses in each direction). The more pulses, the more sensitivity, at the expense of a lower update rate in the image and less ability to see rapid variations. 
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A variant of color Doppler is where only the power of the Doppler signal is depicted (Power Doppler). This gives higher sensitivity, but less quantitative information and no information about direction. This gives particularly good visualiztion of the small blood vessels in organs such as kidneys. 
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A good color Doppler requires a filter that separates stationary measures from movable ones. It separates the strong tissue signal, with low relative velocity, from the significantly weaker signal from blood. This filter's parameters can be adjusted indirectly by the user.